The production of chloranil from hydroquinone (1,4-dihydroxybenzene) or 1,4-benzoquinone or chlorinated 1,4-benzoquinone by the following processes, described in the literature, is known per se:
1. Chlorination of hydroquinone with concentrated hydrochloric acid and concentrated hydrogen peroxide in the presence of magnesium chloride (German Offenlegungsschrift 2,645,114); PA1 2. Action of chlorine on hydroquinone in boiling concentrated hydrochloric acid (Chemiker Zeitung 56 (1932), page 569); PA1 3. Action of hydrochloric acid and nitric acid (aqua regia) on hydroquinone (J. Chem. Soc. Japan 63 (1942), page 1441); PA1 4. Reactions of antimony(V) chloride with hydroquinone (Chemiker Zeitung 104 (1980) No. 1, pages 13 and 14; PA1 5. Action of hydrogen chloride, air and metal salts on hydroquinone (East German Pat. No. 29,292); PA1 6. Reaction of trichloro-1,4-benzoquinone with chlorine in the presence of iodine and water (Liebigs Annalen der Chemie, supplementary volume 6 (1867), 213); PA1 7. Treatment of a mixture of trichloro-1,4-benzoquinone and tetrachloro-1,4-benzoquinone with hydrogen chloride in glacial acetic acid and subsequent action of concentrated nitric acid (Beilstein 7, 637); PA1 8. Action of concentrated hydrochloric acid and 35% hydrogen peroxide on 1,4-benzoquinone (Ann. Chimica applic. 22 (1932), 602; PA1 9. Introduction of chlorine into a solution of hydroquinone in aqueous hydrochloric acid with added chromium trioxide (Naugatuck Chem. Comp., USA, German Pat. No. 594,520, Friedlander 20, 2047, U.S. Pat. No. 1,918,328). PA1 Re 1: A very large excess of hydrochloric acid (96 times the molar quantity) is required, and a very high salt load results due to the addition of 7.4 times the molar quantity of magnesium chloride. Furthermore, the prescribed temperature/time control during the addition of hydrogen peroxide cannot be maintained because of the high heat of reaction. A repeat of this process using only 30 times the molar quantity of hydrochloric acid, 3 times the molar quantity of magnesium chloride and more suitable temperature control gave a qualitatively poor chloranil (melting point 215.degree.-220.degree. C., yield 95% of theory) with trichloro-1,4-benzoquinone and tetrachlorohydroquinone as impurities. PA1 Re 2: The introduction of gaseous elementary chlorine into boiling concentrated hydrochloric acid leads to an extensive escape of elementary chlorine gas into the hydrogen chloride vapors and makes it necessary to use a large excess of chlorine. PA1 Re 3: In this process, about 25 times the molar quantity of mineral acid, composed of 15 times the molar quantity of hydrochloric acid and about 10 times the molar quantity of nitric acid, is used. The yield is only about 45-65% of theory (melting point 280.degree. C.). There is no indication regarding the disposal of the excess acid (in particular of the nitric oxides). PA1 Re 4: The use of antimony is toxicologically objectionable and requires expensive recovery. Moreover, phosgene is said to be formed in this process. PA1 Re 5: In the cited patent itself, attention is drawn to the high consumption of auxiliaries and to the low yield. Moreover, the steam distillation consumes a lot of energy. PA1 Re 6: The use of iodine makes the regeneration of the hydrochloric acid for re-use more difficult. PA1 Re 7: The stagewise synthesis from quinone (here: trichloro-1,4-benzoquinone) and hydrochloric acid with subsequent oxidation (here: nitric acid) of the chlorinated hydroquinone (here: tetrachlorohydroquinone) to give the quinone, with the necessary interstage purification operations, is an extremely time-consuming process and is unsuitable as an industrial process. PA1 Re 8: In the process, an initial treatment with concentrated hydrochloric acid (22 Be =37%) (11 times the molar quantity) for 20 hours is followed by a treatment with 35% hydrogen peroxide below 60.degree. C. for 12 hours. Even though a high yield of chloranil (melting point 289.degree. to 290.degree. C.) is obtained, the production becomes very expensive because of the low space-time yield). PA1 Re 9: In the process, hydroquinone in hydrochloric acid is oxidized with chromium (VI) oxide (20 g/mol) to quinhydrone and the latter is then chlorinated with elementary chlorine to chloranil, initially at 25.degree. C. and finally while hot. In the light of the present demands for protection of the environment, the use of chromium (VI) oxide is no longer tolerable economically.
These known processes have, however, the following disadvantages:
The possibility of working under pressure (in an autoclave), not indicated in the quoted literature reference, requires greater engineering and safety efforts (fully enameled fittings, valves and pipe connections).
The quantity of 37% hydrochloric acid indicated there (28 times the molar quantity) is very high, but is evidently insufficient for obtaining a reaction mixture which can be stirred at 25.degree. C. Under these conditions, the mixture solidifies with the formation of tetrachlorohydroquinone.
The above review of the state of the art shows that the known processes generally require a large excess of hydrochloric acid, in some cases even auxiliaries which pollute the environment, and unusual oxidizing agents as well as long reaction times.